A third solution strategy that has been popular during many years, is a combination that approximates radiation damping via the BEM technique, while the scatterer, (including heterogeneities and/or nonlinearities), is treated with an FEM algorithm [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}. That approach becomes especially attractive when the BEM discretization is written in the form of a displacements-based finite element, representing the semi-infinite domain as a half-space-super-element (HSSE) and favouring its straightforward coupling to a finite element model for the scatterer. Although the coupling of BEM and FEM algorithms can be accomplished in a wide majority of commercially available finite element codes that assimilate user element subroutines, e.g., [10]}, [11]}, the asymmetric and dense character of the HSSE-coefficient-matrix still restrains the advantages of the finite element method. Therefore, additional modifications must be imposed to the resulting radiation boundary approximation, in order to obtain an efficient and accurate formulation that preserves the nice properties of the finite element method. In this work we enforce the HSSE-coefficient-matrix to remain banded and symmetric, and asses the effect upon the solution accuracy of such compression scheme.
